1. Field of the Invention
This invention relates to a process for coating substrates with polyurethane ureas and to the substrates thus coated.
2. Description of the Prior Art
It is known that sheet-form textiles can be coated with polyurethane urea solutions containing up to 75% by weight solvents. It is possible to use either fully reacted polyurethane ureas or polyurethane ureas which have to be post-crosslinked with a second component to develop their coating properties. Coating compositions of this particular type are described, for example, in U.S. Pat. No. 3,711,571. In this case, dissolved polyurethane ureas are mixed with oxime-blocked NCO prepolymers and the resulting mixture is hardened during a heat treatment in a drying tunnel. Accordingly, a crosslinker has to be added during preparation of the spreading or coating paste.
GB-PS No. 970,459 describes a process for bonding a foam sheet to a textile substrate. The adhesive coating consists of a reactive mixture consisting essentially of a ketoxime-blocked NCO prepolymer and N,N,N',N'-tetrakis-(2-hydroxypropyl)-ethylene diamine as crosslinking agent. This system hardens through urethane groups and not through urea groups. In this case, too, a reactive component has to be added to the spreading paste before processing.
DE-OS No. 2,902,090 (U.S. Pat. No. 4,248,756) describes two-component coating systems of ketoxime-blocked prepolymers and, inter alia, 4,4'-diamino-3,3'-dimethyldicyclohexylmethane as crosslinkers/hardeners containing .ltoreq.15% by weight solvent in the preparation. The crosslinking reaction takes place in a single step at temperatures of 120.degree. to 190.degree. C. and preferably at temperatures of 140.degree. to 170.degree. C. Coating systems of this type undergo a pronounced heat-induced reduction in viscosity before the reaction of the blocked NCO prepolymer with the crosslinking polyamine. This reduction in viscosity presents penetration problems in direct coating and lamination which have to be overcome by special measures.
It is an object of the present invention to provide a process for coating substrates with polyurethane ureas which obviates the disadvantages of known coating processes.